I've written a little plugin for using AJAX Comments based on the small and fast jQuery-Framework.
The main reason was, that all other solutions on this are based on prototype/scriptaculous which are very huge compared to jQuery and the jQuery-Syntax is very smart and easy to learn. I didn't found any plugins or descriptions how to set up AJAX-Comments with jQuery, so maybe some of you find this plugin useful. You may download it here:
My blogentry is written in german, but in the ZIP-Package a short readme.txt with english installation instructions is included.